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4 Neuroscience > L3 Somatosensation/Pain > Flashcards

L3 Somatosensation/Pain Flashcards

1
Q

Sensory transduction

A

process of converting energy of a stimulus into an electrical signal

similar in all somatosensory afferents
stimulus alters the permeability of cation channels in afferent nerve, creating a receptor potential

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2
Q

Type of neurons in somatosensory system

A

pseudounipolar
reside in the dorsal root ganglion
allows for the electrical activity to “skip” the cell body on its way to the target

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3
Q

receptor potential

A

depolarizing current in afferent nerve endings
has to be a high enough magnitude or have a strong enough stimulus to reach threshold

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4
Q

Free nerve endings

A

afferent fibers that lack specialized receptor cells have free nerve endings

especially important in pain

mechanoreceptors would be an example of a specialized receptor cell

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5
Q

Proprioception afferent nerve characteristics

A

Receptor type: muscle spindle
Axon type: Ia, II
Largest diameter, fastest speed

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6
Q

Touch afferent nerve characteristics

A

Receptors: merkel, meissner, pacinian, ruffini
Axon: A-Beta
smaller diameter and slower speed then proprioception

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7
Q

Pain/Temperature afferent nerve characteristics

A

Receptor: free nerve endings
Axon: A-delta
smaller diameter and slower speed then touch

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8
Q

Pain/Temp/Itch/Non-dscriminative touch afferent nerve characteristics

A

Receptor: free nerve endings, unmyelinated
Axon: C
smallest diameter, slowest speed

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9
Q

Merkel afferents

A

slow adapting, enriched in finger tips. Signal the tactic aspect of a touch stimulus, such as pressure

detailed, best for braille

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10
Q

Meissner afferents

A

rapidly adapting fibers that innervate skin more densely then Merkel. Large receptive fields, transmit signal with reduced spatial resolution

good at detecting relatively low-frequency vibrations that occur when textured objects are moved across the skin

detects slippage between skin an an object held in the hand

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11
Q

Pacinian afferents

A

rapidly adapting fibers
detect vibrations transmitted through objects that contact the hand or are being grasped in the hand

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12
Q

Ruffini afferents

A

slow adapting
responsive to skin stretches

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13
Q

Rapidly adapting afferents

A

fire rapidly when a stimulus is first presented, then fall silent in the presence of continued stimulation

effective in providing info about changes in ongoing stimulation

Pacinian & Meissner

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14
Q

Slowly adapting afferents

A

generate a more sustained discharge in the presence of ongoing stimulus

better suited to provide info about spatial attributes of the stimulus, like size and shape

Ruffini and Merkel

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15
Q

Proprioceptors

A

provide info about mechanical forces arising from within the body itself

examples include muscle spindles, golgi tendon organs, joint receptors

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16
Q

Muscle spindles

A

-found in majority of striated muscles
-consist of specialized intrafusal muscle fibers surrounded by a capsule of connective tissue
-arranged with extrafusal fibers of skeletal muscle
-when the muscle is stretched, the tension on the intrafusal fiber activates mechanically gated ion channels in nerve endings

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17
Q

Golgi tendon organs

A

-low-threshold mechanoreceptors in tendons that inform the CNS about changes in muscle tension

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18
Q

DCML Pathway

A

carries light touch and proprioception
1. information travels via dorsal root through gracile fasciculus or cuneate
2. Synapses on gracile nucleus
3. Decussates in the arcuate fibers
4. Travels up the medial leminscus
5. Synapses on the VPL
6. Travels through the internal capsule, corona radiata, to end at SI

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19
Q

Hierarchy of somatosensory cortex

A

S2 is dependent on the activity in S1
S2 sends info to limbic structures

S1 also sends info to Broadman areas of 5 and 7, which supply inputs to the frontal lobe. Help to integrate information from sensory to motor cortex

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20
Q

Nociceptors

A

initiate the sensation of pain
arise from cell bodies in dorsal root ganglia
end in free nerve endings
conduct slowly
usually lightly myelinated or unmyelinated
usually A delta or C group axons

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21
Q

First pain

A

sharp
A-delta fibers usually convey this feeling

22
Q

Second pain

A

delayed, diffused, long lasting
C-fiber convey these

23
Q

A-delta fibers

A

convey first pain
has two classes that respond to heat at different levels

Type 1 = dangerous heat, low mechanical
Type 2 = Low heat, high mechanical

24
Q

C-fibers

A

most respond to all nociceptive stimuli, making them “polymodal”

25
Q

Nociceptors vs Thermoceptors

A

Action potentials are fired at same rate at all temps at thermoreceptor

number and frequency of firing increase at nocicoceptors

26
Q

Capsaicin

A

Found in peppers, activates responses in C fibers

the less TRPV1 receptors you have, the more spice you can handle

27
Q

ALS Pathway

A
  1. Free nerve ending
  2. Lissauers Tract*
  3. Decussate in ventral commisure
  4. Synapses in Medulla, Pons on RF and Midbrain on PAG
  5. Remaining fibers travel up and synapse in thalamus on MD, VPL, VMP
  6. MD –> Cingulate gyrus, VPL –> SI, VMP –> insula
  • some fibers travel up to raphe nuclei to then synapse on the PAG
28
Q

Rexed’s laminae

A

descriptive divisions of spinal gray matter in cross section

process and transmit sensory info, coordinate motor functions

C fibers will terminate on Rex I/II
A delta will terminate on Rex I/V

I/V = brainstem and thalamic
Non-nocioceptive = III/IV/V

29
Q

Wide dynamic range neurons

A

Multimodal lamina V neurons are known as this

some receive visceral sensory input as well as pain inputs

could be an explanation for referred pain

30
Q

Spinal cord lesion

A

Unilateral spinal cord lesion

Loss of ALS (pain, temp, itch) on CONTRALATERAL side

Loss of DCML (sensation, touch, pressure, etc) on IPSILATERAL SIDE

this is because in the ALS the 2nd order neurons in I and V cross midline and ascend to brainstem vs DCML, they cross in medulla

31
Q

Sensory discriminative pain

A

gives us location, intensity, quality of noxious stimuli

Depends on info relayed through the VPL to S1 and S2

ALS tract manages it

32
Q

Affective-motivational pain

A

unpleasant feeling, fear, anxiety, fight or flight response

targets: reticular formation, PAG, superior colliculus, parabrachial nucleus

33
Q

Parabrachial nucleus

A

processes and relays second pain to amygdala, hypothalamus, thalamic nuclei

help to elaborate affective-motivational aspects of pain

34
Q

ALS and absence of DCML

A

ALS is capable of mediating something like nondiscriminative touch, but stereognosis is impaired and it lacks fine spatial resolution

C fibers do this

35
Q

Other modalities of ALS

A

responsible for innocuous temperature sensation, which are mediated by fibers that don’t respond to noxious stimulus or mechanical stimulation, just change in temp

cells in lamina 1 cause the actions that relate to homeostasis

36
Q

Hyperalgesia

A

following a painful stimulus that caused tissue damage

stimuli in area of injury are seen as significantly painful, when they should be slightly painful

37
Q

Peripheral sensitization

A

results from interactions nociceptors with the inflammatory soup of substances released at tissue damage

heightened sensitivity of nerve endings and an increased responsiveness to pain signals

These substances/molecules cause the nerve endings to become sensitized, making them more likely to respond to low level stimuli

38
Q

Purpose of peripheral sensitization

A

protecting the injured area
promote healing
guard against infection

39
Q

Central Sensitization

A

rapid onset, activity-dependent increase in the excitability of neurons in the dorsal horn of the spinal cord

triggered by activity at nociceptors in dorsal horn

causes increase in pain and sensitivity in the CNS

causes subthreshold levels of activity to be sufficient to generate APs in dorsal horn neurons

40
Q

What type of sensitization is the underlying process for developing chronic pain?

A

central

41
Q

Allodynia

A

induction of pain by a normally non-painful stimulus

occurs immediately after painful event and can outlast the pain of the stimulus by several hours

42
Q

What contributes to central sensitization?

A

Windup

progressive increase in the discharge rate of dorsal horn neurons in response to repeated low-frequency activation of nociceptive afferents.

EASIER: refers to an amplified and prolonged pain response in the spinal cord

lasts only during stimulation and happens b/c of summation of slow synaptic potentials

the delta stimulus remains strong because there is a increased sensitivity to glutamate

43
Q

Neuropathic pain

A

when afferent nerve fibers or central pathways are damaged, sensitization can persist causing neuropathic pain

can arise without stimulus or can be produced by a mild stimulus

constant burning sensation that can have shooting, stabbing, or jolts

no inflammation process

44
Q

Phantom limbs/pain

A

most common cause of chronic pain syndromes

possibly due to maladaptive plasticity in neural circuits

reorganization of mapping/neural plasticity, residual nerve activity, central sensitization can cause it

45
Q

Pain modulation

A
  1. PAG–> can produce analgesia, inhibits nociceptive neurons in dorsal horn of SC
  2. Parabrachial nucleus, dorsal raphe, locus ceruleus, medullary RF –> release NTs that can excite or inhibit neurons
  3. Descending tracts–> excite or inhibit dorsal horn, impact efficacy of nociceptive transmission
  4. Interactions between mechanoreceptive afferents and neural circuits (rubbing toe after hitting it)
46
Q

Gate theory of pain

A

flow of nociceptive info through the SC is modulated by activation of large myelinated fibers of low-threshold mechanoreceptors

47
Q

Placebo effect

A

responses can be blocked by antagonist opioids (in the example of pain medication), there is a physiologic basis for pain relief experienced–pts pain is real

causes activation of endogenous opioid receptors, also can activate descending pathways which modulate pain

48
Q

Endogenous Opioids

A

located in the PAG
three types: enkephalins, endorphins, dynorphins

areas of the nervous system that produce analgesics are very receptive to opioids, meaning there are opioid sensitive neurons

these substances reduce the level of activity passed onto higher processing centers

49
Q

Endogenous cannabinoids

A

thought to decrease the release of neurotransmitters, so essentially modulating neuronal excitability

cannabinoids can block the electrical stimulation of the PAG, stopping pain signals from traveling elsewhere

noxious stimuli cause increased cannabinoids in PAG

50
Q

PAG roles in Pain

A
  1. pain inhibition, causes release of opioids
  2. Descending tract modulation
  3. Modulates emotional response to pain
  4. Placebo effect
  5. Integrates sensory and emotional information to modulate pain

4 Neuroscience (9 decks)

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